Centrifugal abrasive throwing wheel



D. C. TURNBULL CENTRIFUGAL ABRASIVE THROWING WHEEL Fil'ed June l1, 1940 2 Sheets-Sheet l INVENTOR l Yjdlfld C' lrd f mm ATTORNEY j Dec.'29, i942. D. c. TURNBULL CEN'IRIFUGAL ABRAS-IVE THROWING WHEEL Filed June ll, 1940 2 Sheets-Sheet 2 from 9,000 to 15,000 lineal feet per minute.

Patented Dec. 29, 1942 UNITED STATES PATENT OFFICE i CENTRIFUGAL THBOWING i David C. Turnbull, Mishawaka, Ind., assignor to The American Foundry Equipment Company, Mishawaka, Ind., a corporation of Delaware Application June 11, 1940, Serial No. 339,869

12 Claims.

This invention relates tocentrifugalabrasive throwing wheels, and more particularly to improved blades for use in such wheels. This application is a continuation ln part of my co-pending .application Serial No. 124,815, filed February 9, 193'7, now Patent No. 2,204,634, dated June 18, 1940, which is a division of my application Serial No. 111,212, filed November 17, 1936, now Patent No. 2,204,633, dated June 18, 1940.

The blades constructedin accordance with this invention are particularly adapted for association with so-called cellular type abrasive throwthe wheels wherein the blades are positioned between and supported by two spaced side wallforming discs. The side wall discs are held in rigid spaced relationship by suitable spacers or studs rigidly fixed to the discs. One of the discs is fixed to a hub secured to a highspeed shaft. The blades extend inwardly short of the axis of rotation of the discs, to define a central space within which is positioned a normally stationary tubular control member or cage. An impeller is positioned within the tubular control cage and fixed to the wheel to rotate therewith. The impeller is provided with throwing vanes or elements equal in number to the blades of the wheel. The impeller is designed to project a stream of abrasive out through a discharge opening in the tubular wall of the control cage and into the path of rotation of the blades when the wheel is rotated.

The. blades are generally channel-shaped in cross-section and the side edges of the blades are designed to seat within paired grooves provided on the inside faces of the side wall discs of the' wheel. These grooves provide shoulder supports for the blades.l The blades are removable through the periphery of the wheel, are held in position by adjustable set screws which engage the side edges of the blades.

The abrasive, normally comprising steel shot or grit, has a severe abrading or cutting action on blades'when the abrasive throwing wheel is rotated at abrading speeds. To develop effec- .tive abrading speed the periphery of the wheel or the outer end of the blades should be rotated Such wheels are generally constructed from eight to twenty inches in diameter, and the wheel is rotated at an R. P. M. to develop such peripheral speed. The blades are further subjected to severe vibration, shock and metal fatigue which they must be designed to withstand and resist if hazardous operating conditions are to be avoided. It is further important that the blades be so designed as to wear evenly and equally or otherwise the wheel will be thrown out of dynamic balance. Free and unobstructed entry of the abrasive onto the inner end of the blades should be permitted, and the abrasive in its. moveand ment outward along the advancing face of the blade should be confined between the side wall flanges thereof but evenly distributed over the width of the advancing face thereof.

An object of this-invention is to provide an improved abrasive throwing blade for use with abrasive throwing wheels, which is designed to pick up the abrasive on the inner ends thereof with a minimum of shock and scattering and which is so proportioned that its e'ective wear life is substantially uniform from one end to the other thereof.

Another object of this invention is to provide an' improved abrasive throwing blade which is designed to effect movement of the abrasive over the advancing face thereof with uniform distribution of the abrasive over the advancing face .of the blade.

Another object of this invention is to providean abrasive throwing blade having vibration damping features.

Still another object of this invention is to provide an abrasive throwing blade of hard wear resistant metal which is internally reinforced so as to increase its resistance to shock, vibration and metal fatigue and overcome the danger of breakage in use.

Another object of this invention is to provide an improved means for locking the blades in firm seating position between the side wall discs of the wheel whereby blade vibration and blade fatigue are materially reduced.

Various other objects and advantages' of this invention will be apparent from the following particular description and from inspection of the accompanying drawings.

While the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which y Fig. 1 is a side view of the abrasive throwing wheel as it appears when assembled, equipped with my improved abrasive throwing blades positioned between the side wall discs of the wheel, certain parts being broken away to more clearly illustrate certain features of the construction;

Fig. 2 is an end view of the wheel as it appears when looking in the direction of the arrows 2--2 of Fig. 1, certain parts being broken away to illustrate certain features of construction;

Fig. 3 is a perspective view of my improved blade showing more particularly the bottom face thereof;

4 is a perspective view of a blade o! somewhat modified form as it appears when looking down on the advancing face thereof;

Fig. 5 is a. perspective view of the blade shown in Fig. 4 as it appears when looking at the bottom face thereof;

Fig. 6 is a transverse cross-sectional view of the blade shown in Figs. 4 and 5 as it appears when positioned between and supported by the side wall discs of the wheel, this view showing a fragmentary portion of the side wall discs oi' the wheel with the improved means for removably locking the blade in position being shown in greater detail;

Fig. 7 is a bottom-face view of a blade oi further modified construction having vibration damping cavities in the bottom face thereof; and

Fig. 8 is a longitudinal cross-sectional view through the blade shown in Fig. 7 as it appears when looking in the direction of the arrows 8 8 of Fig. 7.

Similar reference characters refer to similar parts throughout the several views of the drawings and the specification.

The centrifugal abrasive throwing wheel w with which my improved blades are particularly designed for use is illustrated in Figs. l and 2 of the accompanying drawings. Such wheel w generally comprises a rear side wall disc I and afront side wall disc 2 which are of substantially the same diameter and which are maintained in xed parallel relationship by a plurality of spaced connecting studs 3 which are iixedly secured to the side wall discs as by welding. The wheel w is fixed to the end of a rotatably mounted high speed shaft 4 fixed to a hub 5,y the hub being secured to the rear side wall disc I by bolts S. The abrasive throwing blades b are positioned between and supported by the side wall discs I and 2 in radially arranged spaced relationship. The blades'b extendl inwardly cf the wheel short of the axis of rotation thereof to provide a central space I.

A tubular control member or cage c extends into the central space 'I and is supported during operation of the wheel in normally stationary position by a suitable support 8. The tubular control member c extends through a suitable circular opening 9 provided in the front side wall disc 2. Abrasive is supplied to the interior of the tubular control cage c by a suitable abrasive vsupply pipe Ill and the abrasive is ejected out through the discharge aperture I I in the tubular side wall of the control cage c by an irnpeller i positioned within the tubular control member. The impeller i generally comprises a plurality of radially arranged vanes I2 which are equal in number tothe blades b of the wheel. The vanes I2 are supported between a rear disc I3 and a front disc I4. The front disc I4 may be provided 'with a circular opening I5 through which the abrasive from the feed pipe may pass into the path of rotation of the vanes I2. It will be noted by referring to Fig. 1 that the wheel as illustrated rotates clockwise and that the advancing face of each impeller vane I2 is positioned slightly in advance of the advancing face of the corresponding blade b. Each impeller vane I2 is designed to pick up a certain quantity of abrasive material during rotation and throw it out through the discharge opening II in the tubular control member and into the path of rotation of the advancing face of the corresponding blade b. The rear wall I3 of the impeller i seats against a circular centering plate I6, which in the rear wall disc I3 of the impeller and a hole in the centering disc I8 and screws into the end of the wheel shaft 4. The centrifugal abrasive throwing wheel above described is widely known A and usedv in the art.

It will be noted that the side wall discs I and 2 of such centrifugal abrasive throwing wheels are provided with paired grooves 2l) which extend from the periphery of each side wall disc I and 2 radially inwardly to a point adjacent the tubular control cage c. These paired grooves provide guideways for the side edges of the blades b which permit their removal through the periphery of the wheel. These grooves, as shown in Fig. 1, are substantially uniform in width throughout and each groove denes a top shoulder portion 2I and a bottom shoulder portion 22. The side edges of thev blade must be so shaped and proportioned as to freely slide within these grooves. Each blade b is preferably held in position bya set screw 23 ,provided in one of the side wall discs or, preferably, a pair of set screws, one provided in each of the sidewall discs I and 2. Each set screw 23 is threaded into a threaded tubular nipple 24 which seats within a suitable aperture in the side wall disc and is sweated or welded to the side wall disc.

v The blades b are generally channel-shaped in cross-section and preferably formed from a wear resisting metal. Each blade generally comprises a bottom wall portion 30 and two generally parallel extending raised side edge-portions 3l. As clearly shown in the drawings, the outside faces of the side edge portions 3I, as indicated at 32 of the drawings, are of uniform height throughout the length of the blade so that these side edge portions-will smoothly fit but freely slide in the grooves 20 provided in the spaced side wall discs I and 2. The bottom faces 33 of the side i edge portions 3i, as indicated in the drawings,

are also of uniform width, permittingY free and unobstructed insertion and removal of the blade into and from the disc grooves 20. The inner end 34 of each side edge portion 3I is also cut substantially square or at right angles to the bottom face 33 thereof, which ends are designed to abut against the centering plate I6 or similar device to limit the inserted position of the blades in the wheel.

The bottom wall portion 30 of each blade has a tapered face 3B at the lower inner end thereof, which provides a relatively thin inner edge 33, which is shaped to.avoid interference with the abrasive ejected from the control cage opening II into the path of rotation of the blades. The face 38 is tapered. at an angle of approximately 45 and thebottom wall portion 30 increases substantially uniformly in thickness from the base of the tapered portion 38 to the outer end of the blade. k

Since the blades are supported in suspended position between the side wall discs I and 2, it is highly desirable that the grooves 20 provide an even, firm and smooth supporting seat for the side edge portions 3| of the blades b. In blades constructed in accordance with this invention, each bottom surface 33 of the side edge portion 3I of each blade is designed to have a smooth seating t with the lower shoulder portion 22 of each groove 2D. The bottom surfaces 33 of the blade side edge portions 3| are so with a rounded nose portion 23 designed to seat within ithe adjacent blade notch 42, and a tool receiving socket 25 within which a manipulating tool may be inserted. It will be noted that when the set screw 23 is tightened, the nose portion 23 thereof. engages the cam surface 43 and serves to press the bottom face 33 of the side edge portion 3| into firm seating engagement with the bottom shoulder portion 22 of the blade receiving groove 20. Thus with this improved form of attachment each blade finds a firm seat upon the shoulder portions 22 of each pair of grooves 23 whereby strains and stresses on the blades and vibration of the blades is materially reduced.

Abrasive throwing blades for use in these abrasive projector wheels are preferably made from cast metal which generally comprises a high grade of iron alloyed with certain special alloys to produce a wear resistant material. Most wear resistant ferrous alloys are relatively brittle. Dangerous operating conditions result if any portion of the blade cracks off during operation because of the high velocity at which the wheel is rotated. Strains resulting from vibration, metal fatigue and abrasive impact, are most severe near the outer end of the blade.-

In accordance with this invention, metal alloys which have the. desired ties though relatively brittle, may be employed in the casting of blades by embedding in the blade transversely extending reinforcing rods or bars of high tensile strength, such as spring steel bars 50. Any desired number of such bars may be provided to extend from the outer end of the blade in spaced parallel relationship toward the inner end thereof. Such bars may be fixed at the ends thereof to thin gauge steel templets 5| so as to maintain the bars in proper spaced relationship until the poured blade metal hardens. The reinforcing assembly comprising the spaced bars 50 attached to templet plates 5|, are set in the drag when the mold is assembled. The molten metal alloy which is to form the blade is then poured so as to ow around and encase the l reinforcing rods 50. The bars 50 should extend transversely through and be buried within the bottom wall portion 30 'and the side wall portions 3| of the blade when cast, and the templet plates 5| maybe positioned so as to lie substantially flush with the outside face 32 of the side edge portions 3| of the blade. The rods 50 are preferably positioned so as to lle within but substantially close to the rear surface of the bottom wall portion 30 Where the tensile strain on the blade structure is normally the greatest. When the blades have been thus reinforced, blade breakage in operation may be greatly reduced or overcome even though the blade is cast from metal'alloys which though highly wear resistant are relatively brittle.

Since the wear on the bottom wall portion 30 of the blade increases during use as the outer end of the blade is approached, the blade may high wear resisting qualibe givenA a relatively uniform wear life if the 75 thickness of the bottom wall portion 3l is correspondingly gradually increased from the inner to the outer end of the blade. Since some of the most desirable wear resistant alloys are relatively expensive, it is desirable that the metal in the blade be so distributed as to obtain maximum wear and substantially uniform wear life throughout. There is shown infFigs. 1, 2 and 3, one form of blade as above described which is generally termed the underslung type, wherein the rear surface of the bottom wall portion 30 gradually bellies below the bottom face 33 of the side edge portions 3| an increasing amount as the outer end of the blade is approached. The bottom wall surface 40 merges with the bottom faces 33 of the side edge portions 3| through inclined surfaces 4|, as indicated in Figs. 2 and 3.

The top face 35 of the bottom wall portion 33 l5 rClatively flat and smooth throughout its length. The side edge portions 3| extend a substantially uniform distance above the top surface 35 of the blade so as to provide abrasive retaining flanges 33 which are of substantially uniform height throughout the length of the blade. The inside faces of flanges 36 merge with the top abrasivereceiving surface 35 of the bottom wall portion through rounded fillet surfaces 31 which are so shaped as not to interfere with the abrasive movement of the blade and yet operate to maintain the abrasive substantially uniformly distributed across the width of the abrasive receiving surface 35.

Blades shaped and constructed as above described and illustrated in Figs. l, 2 and 3, possess maximum strength where the greatest strain is imposed, without excessiveuse of metal which would otherwise make the blade unnecessarily heavy and expensive to manufacture. The crosssection of the blade adjacent the outer end the! eof where the vwear and strain are greatest, is substantially uniform throughout the side edge portions 3i and the bottom portion 30, as illustrated in the blade shown in cross-section in Fig. 2. The blade may be firmly locked between the side wall discs l and 2 of the wheel by tightening the set screw 23 and when tightened the bottom faces 33 of the side edge portions 3l are pressed into close seating engagement with the shoulder portions 22 of the grooves 2li provided in the side wall discs, a feature which materially reduces blade vibration and metal fatigue. By the provision' of the reinforcing rods 50 excessive strains are removed from the wear resistant metal of which the blade is composed and transmitted to these rods of high tensile strength, which are fully vable to carry such strains. Since the rods 50 are positioned adjacent the lower or rear surface 40 of the bottom wall portion 30 the abrasive receiving surface 35 may be worn away approximately half or less than half the thickness of the bottom wall portion 30 before the reinforcing rods 50 are reached, by which time the blade is considered worn out and no longer safe for use.

The blade illustrated in Figs. 4 and 5 is substantially similar to the blade illustrated in Figs. l and 2 and 3, except that the bottom wall portion 30 has a relatively flat abrasive receiving surface portion which extends approximately half the length of the blade and which merges with the side wall portions 3l in relatively smooth curved surfaces 46 of small radius. The outer half 45' of the top wall surface is' relatively rounded in contour but merges smoothly with the relatively flat top wall surface portion 45. The

outer surface portion 45' also merges with the side edge portions 3| in curved surfaces 48' which have a curvature radius substantially greater than the curvature radius ofthe surface 4B. When the blade is provided with such a top wall surface, the abrasive moving rapidly over the relatively flat top surface portion 45 is caused to c'ontract into a narrowing stream so that the abrasive discharged from the blades is concentrated in a stream of relatively narrow width. Such blades are particularly desirable where it is desired to throw an abrasive stream of high abrading power but concentrated over an area of relatively narrow width.

The rear surface of the blade shown in Figs. 4 and 5 has a relatively flat surface portion 41 adjacent the inner end thereof which merges into a relatively rounded belly portion 4l at the outer end of the blade. The bottom wall portion 3B of this blade increases substantially uniformly in thickness from the inner to the outer end thereof and, as shown in Fig. 5, the bottom wall portion 36 and the side wall portions 3i at the outer end of the blade are of substantially uniform thickness throughout. The reinforcing bars 513 provided with this blade are shaped to substantially conform to thebottom bellied surface 66 of the blade and are cast into the blade metal as closely as permissible to the outer bellied surface l'l so that maximum blade wear and maximum blade strength is attained.

Abrasive throwing blades b designed for use in Wheels, of the type shown in Figs. 1 and 2 are made in lengths and widths to properly nt the wheel. If the wheel is only eight inches in outside diameter, blades approximately only 21/2 inches to three inches in length would be used; while wheels having an outside diameter of approximately twenty inches would require blades seven to eight inches inA length. The abrasive throwing capacity of the whe'el may be greatly increased by widening the wheel, i. e., increasing the distance between the side wall discs l and 2. For example, a wheel of approximately twenty inches in diameter whose side wall discs I and 2 are spaced approximately 3/4 of an inch, providing blade throwing surfaces of only 3A, of an inch in width, would fire in the nature of fifty to seventy-five pounds of abrasive per minute. If the effective blade width is increased to 21/2 inches, such a wheel would effectively re up to ve hundred pounds of abrasive per minute. If the effective blade width were increased to five inches, for example, `as much as two thousand pounds of abrasive per minute would be red.

It is appreciated that the Wider the blade is made the more serious the strains resulting from vibration become. There is shown in Figs. 7 and 8 a blade which is relatively wide with respect to its length. This blade is provided with a series of shallow cavities or indentations in the rear surface 55 of the bottom wall portion. 'I'hese shallow cavities or indentations are remarkably effective in damping or reducing vibration, in relieving shrinkage strains when the blades are cast, in reducing the porosity of the thick sections, in inuencing the flow of molten metal in the mold whereby even distribution of the metal in the mold is obtained, in avoiding overlapping or cold shuts when 'the molten metal is poured at a relatively low temperature into a cold mold, and which in general materially reduces possibility of failure of the b'lade in service and materially reduces the weight of the blade. VAs

showninFigs.7 andsforpurpose of illustration, the cavities may be arranged in a series of staggered rows Il, l1, I8, l and n, each row of cavities increasing slightly 'in depth toward the outer end of the blade. While/rounded cavities, as shown in Figs. 'I and 8, appear to be generally preferable, square or diamond shaped cavities which run either parallel to the side of the blades or in a crosswise or diagonal direction may be used. It will be appreciated that such vibration-damping cavities may also be provided in the rear surface 40 of the blade shown in lllg.`

3 and the rear surfaces 41 and 41' of the'blade shown inFlg.5. v p l While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

`What is claimed is:

1. In combination with an abrasive throwing wheel comprising rotatably mounted side wall members; removable and replaceable channel shaped throwing blades positioned between said side wall members, each of said bladesw having a bottom wall portionkand side flange portion seatinside faces of said side wall members, and means ing within corresponding paired grooves on the for removably locking said blades in operative position between said side wall members including, a set 'screw extending through a threaded opening in one of said side wall members adjacent a side flange portion of each blade, the adjacent side flange portion of each blade having a notch cut in the outside face thereof adapted to receive the end of said set screw, said notch extending from the top edge to the bottom edge of said side flange portion and presenting a. substantially straight outwardly and downwardly inclined wedge shaped wall portion against which said set screw may be wedged to drive the bottom face of the adjacent side edge of the blade into firm seating engagement with the adjacent supporting edge of said groove.

2. In combination with an abrasive throwing wheel comprising rotatably mounted side wall members, removable and replaceable channel shaped throwing blades positioned between said side wall members, each of said blades having a bottom wall portion and side ange portions whose lower edges are arranged to seat upon paired shoulder portions provided on the inside faces of said side wall members, and means for removably locking said blades in operative position between said side wall members including, set screws extending through threaded openings in each of said side wall members positioned adjacent the flange portions of said blades, each ange portion of each blade having a notch cut in the outside face thereof adapted to receive the end of the adjacent set screw, eachnotch extending from the top edge to the bottom edge ofthe flange portion and presenting an outwardly and downwardly inclined wedge shaped wall portion against which said set screw vmay be wedged to drivethe bottom face of the adjacent side edge of the blade into firm seating engagement with the adjacent shoulder portion.

3. In combination with an abrasive throwing wheel comprising rotatably mounted side wall members, a removable and replaceable channel shaped throwing blade positioned between said side wall members, said blade having a bottom wall portion and side flange portions Vseating within corresponding grooves on the inside faces of said side wall members, and means for removably locking said blade in operative position between said side wall members including, a tubular sleeve extending through and fixed within an opening in one of said side wall members adjacent a side edge of said blade, a set screw having a rounded end threaded into said tubular sleeve, the adjacent flange porton of said blade having a notch cut in the outside face thereof adapted to receive the rounded end of said set screw, said notch extending from the top edge to the bottom edge of the flange portion and presenting a substantially straight outwardly and downwardly inclined wedge shaped wall portion against which the rounded end of said set screw may be wedged to drive the bottom face of the adjacent side edge of the blade into rm seating engagement with the adjacent supporting edge of said groove.

`4. A blade for use in an abrasive throwing wheel, having a bottom wall portion and abrasive retaining side wall portions, said blade being cast from a wear resistant metal, and reinforcing rods formed from metal of high tensile strength cast into the metal forming the bottom portion of said blade, the adjacent ends of said rods being connected by templets embedded in the wear resistant metal.

5. A blade for use in' an abrasive throwing wheel, having a bottom wall portion and abrasive retaining side wall portions, saidl blade being cast from a wear resistant metal, and a plurality of reinforcing rods formed from metal of high tensile strength cast into the metal forming the bottom portion of said blade and extending transversely thereof, the adjacent ends of said rods being connected by templets embedded in the wear resistant metal.

6. A blade for use in an abrasive throwing wheel having a bottom wall portion and abrasive retaining side wall portions, said blade being cast from a wear resisting metal, and reinforcing asdepth from the inner to sembly cast into the metal forming the blade.

said assembly including a metal templet embedded within each of said side wall. portions, and` a plurality of spaced reinforcing rods formed from a metal of high tensile strength having the ends thereof secured to said templet, said rods extending transversely through the bottom wall portion and into the side wall portion -of said blade.

'1. A blade for use in an Aabrasive throwing wheel, cast from a wear resistant metal and generally channel shaped in cross-section to define bottom wall portion and abrasive retaining side wall portions, said bottom wall portion having a plurality of relatively shallow vibration damping cavities in the under surface thereof defining therebetween an interconnected network of thicker reinforcing metal.

8. A blade for use in an abrasive throwing wheel, cast from a wear resistant metal and generally channel shaped in cross-section to define a bottom wall portion and abrasive retaining side wall portions, said bottom wall portion having a plurality of rows of relatively shallow vibration damping cavities in the under surface thereofv dening therebetween an interconnected network of thicker reinforcing metal.

9. A blade for use in an abrasive throwing wheel, cast from a wear resistant metal and generally channel shaped in cross-section to denne a bottom wall portion and abrasive retaining Iside wall portions, said bottom wall portion increasing in thickness substantially uniformly from a point adjacent the inner endl to the outer end thereof, said bottom wall portion having a plurality of relatively shallow vibration damping cavities, in the under surface thereof defining therebetween an interconnected network of thicker.y reinforcing metal, said cavities increasing in the outer end of said bottom wall portion.

10. A blade for use in an abrasive throwing wheel, cast from wear resistant metal comprising, a pair of similar side wall portions and a bottom wall portion extending between said side wall portions, said side wall portionsbeing substantially straight and of substantially uniform height throughout, said side wall portions presenting substantially flat outside faces, said bottom wall portion having theinner end thereof tapered forwardly in the directionof rotation to present a relatively thin abrasive receiving edge.

said bottom wall portion increasing substantially uniformly in thickness from adjacent said ta'- pered arealto the outer end of the blade, one of said side wall portions outside face thereof adapted to receive' the end of a set screw, said notch extending from the top edge to the bottom edge of the side wall portion and presenting an outwardly and downwardly inclined wedge shaped wall portion against which the end of the set screw may be wedged whereby to drive the blade in the direction of the lower seating edges of the side wall portions.

.11.A blade for use in an abrasive throwing wheel, cast from wear resistant metal comprising, a bottom wall portion, substantially straight side wallportions of substantially uniform height throughout, said side wall portions presenting substantially flat outside faces, said bottom wall portion having the inner'l end thereof tapered forwardly in the direction f rotation .to present a relatively thin abrasive receiving edge, said bottom wall portion increasing substantially unlformly in thickness from adjacent said tapered area to the outer end of the blade, each of said side wall portions having a notch in the outside face thereof adapted to receive the end of a set screw, each of said notches extending .from the top edge to the bottom edge of the side wall portion and presenting a substantially straight outwardly and downwardly inclined wedge shaped wall portion against which the end of a set screw may be wedged whereby to drive the blade in the direction oi' the lower seating edges of the side wall portions.

12. A blade for use wheel, cast from a wear resistant metal and generally channel shaped in cross-section to definea bottom wall portion and similar abrasive retaining side wall portions. said side wall portions being of substantially uniform height throughout, said bottom wall portion increasing in thickness substantially uniformly from the inner to the outer end thereof, the inside faceof said bottom wall portion being substantially flat for a portion lof its length adjacent the inner end of the blade and rounded for a portion of its'length adjacent the outer end of the blade, the outside surface of said bottom wall portion being underslung below 'the vadjacent lower edges of said side wall portions at the outer end thereof.

DAVID C. TURNULL.

having a notch in the in an abrasive throwing 

